This invention relates to the field of bioreactors for cultivation of microalgae or cyanobacteria.
Mass cultivation of microalgae or cyanobacteria has a great potential for modern agriculture, biochemistry and pharmaceutics.
Algal species: Spirulina, Dunaliella and others present important sources of vitamins, proteins, unsaturated fats, organic compounds of iron and other microelements. The most common forms of microalgae or cyanobacteria cultivation photobioreactors are open ponds or open raceways channels.
There are some technical problems connected with application of such systems:
a) Light distribution within photobioreactors constructed as ponds or channels presents a serious problem. The depth of the pond or raceway channels should be in the range of 15/30 cm.
It determines in turn relatively low final microalgae (or cyanobacteria) concentration in nutritious solution and high cost of harvesting microalgae biomass.
b) Mixing the nutritious solution in order to prevent cell sinking, and, in addition, to remove from the nutritious solution the generated oxygen, which inhibits photosynthesis process.
c) It is necessary to provide an adequate amount of CO.sub.2, which is required for performance of photosynthesis process; this CO.sub.2 is supplied as a rule from the ambient air or from gaseous medium enriched with CO.sub.2 by its dissolution in the nutritious solution.
d) Maintenance of optimum ranges of daily and nightly temperatures of the nutritious solutions.
There are patents and patent applications, which are devoted to solve a part of the above-mentioned problems; however, these patents and patent applications do not provide sufficiently effective and cheap solutions of the described problems.
U.S. Pat. No. 4,084,346 describes a system of channels intended for algae growing; there are discharge means installed in these channels which introduce CO.sub.2, into the microalgae suspension.
U.S. Pat. No. 3,468,057 describes a basin for culture of algae in an aqueous nutrient medium comprising, in combination, at least two illuminated horizontal zones, at least two inclined zones and at least one gas injection means.
U.S. Pat. No. 3,955,317 describes a method for growing plant cells containing chloroplasts in liquid suspension simultaneously with the growth of photosynthetic bacteria, in which method the liquid suspension containing the plant cells is enclosed in a first elongated, at least partially transparent, container and a liquid suspension of photosynthetic bacteria is contained in second elongated, at least partially transparent, container, the said second container being attached to the said first container so that light passing through the said first container then passes through the said second container; the said containers preventing passage of liquid from one container to the other, the containers being supported on a body of water; the liquid suspension in the first container being exposed to light and brought into contact with carbon dioxide.
U.S. Pat. No. 3,998,186 describes a method and apparatus for shrimp culture; shrimp hatched and brought through larval and post-larval stages environment unit which includes plastic cover means positioned over an elongated waterway containing seawater, or the like, and algae in substantial amounts. The design of the unit and the technique of intermittently supplying seawater allows the control of light intensity and light spectral characteristics within the shrimp growing area and the control of seawater flow rate, temperature and dissolved oxygen content of the seawater in the waterway.
U.S. Pat. No. 5,443,985 describes a bioreactor for culturing living cells, particularly shear sensitive cells, wherein the bioreactor is composed of a stationary vessel with opposite spaced walls inclined at an angle to form upper and lower walls. Liquid culture medium and cell culture, such as hybridoma cells, are introduced into the vessel and gas is introduced at the lower end of the vessel to form gas bubbles which travel upward along the upper wall of the bioreactor to disengage from a small portion of the gas liquid interface. The gas bubbles circulate the cells and liquid medium, maintaining the cells in suspension and lifting them in a circulating path upwardly parallel to the upper wall and downward along the lower wall. The bioreactor design thus achieves bulk mixing and aeration by maintaining a significant degree of segregation between the upwardly travelling bubbles and the cells in the liquid medium avoiding unnecessary cell damage by fluid-mechanical shear or by bubble bursting events.
U.S. Pat. No. 5,534,417 describes a method of growing microalgae, which uses the outdoor sunlight as a source of energy. Growth is confined to an assembly of vertical, transparent tubes through which nutrient and air is carried with carbon dioxide. The microalgae is periodically harvested from the tubes.
U.S. Pat. No. 5,741,702 describes a reactor vessel for processing gases containing carbon dioxide by means of a fluid containing algae; this reactor vessel comprises: a first elongated duct having a rectangular cross section with a top surface and a bottom surface for containing said gases and said fluid containing algae; a second elongated duct, abutting said first elongated duct, having a rectangular cross section with a top surface and a bottom surface, said duct having ribs extending from said bottom surface to said top surface to form a plurality of elongated channels for insulating said first elongated duct; wherein the channels of said second elongated duct are constructed so as to be evacuated to create a vacuum therein.
U.S. Pat. No. 5,846,816 describes a bioreactor for biomass production comprising: a substantially transparent chamber, the chamber being at least suitable for containing biomass in a liquid phase, and having a base portion, an upper portion and a number of side walls between the base portion and the upper portion, the side walls being configured so as to generally diverge from the base portion towards the wider upper portion; and circulating means for circulating the contents of the chamber, wherein the circulating means creates a motive force within the liquid phase sufficient to ensure continual mixing of substantially all of the biomass and at least cyclical exposure of biomass to a light source.
U.S. Pat. No. 5,981,271 describes process of outdoor thin-layer cultivation of algae in which suspension of algae saturated with carbon dioxide and enriched with necessary nutrients, is distributed on inclined cultivation areas where the suspension of algae is distributed on inclined cultivation areas under turbulent flow which depends on velocity of flow, on coefficient of roughness of the cultivation surfaces, on the thickness of the algal suspension layer and on inclination of the cultivation surface. Between individual cultivation areas carbon dioxide is supplied into the suspension and the suspension flowing from the lowest cultivation area is conveyed into the collecting tank from which it is pumped on the upper edge of the highest cultivation area. Bioreactor for accomplishing the mentioned process is composed of at least two individual cultivation meandering areas where the lower end of the upper area and the beginning of the next lower area, inclined in the opposite direction, are connected by channels in which outlets for supply of carbon dioxide into suspension are placed.
U.S. Pat. No. 8,110,395 describes a photobioreactor system comprising: a plurality of interconnectable photobioreactor sections which, when connected together, form at least one longitudinally-oriented photobioreactor unit of the photobioreactor system, the photobioreactor sections each comprising a liquid flow channel, and a light-transparent cover that forms a gas headspace between the cover and the liquid flow channel, the cover being constructed and arranged to cover at least a substantial portion of the liquid flow channel and configured to provide the gas headspace even when a gas pressure within the photobioreactor unit is less than the atmospheric pressure surrounding the photobioreactor section, at least one photobioreactor unit of the photobioreactor system further including an evaporative cooling area, including a reservoir and a sprayer, the evaporative cooling area being disposed outside of the cover such that the reservoir is open to the atmosphere outside of the cover, the reservoir being in fluid communication with the liquid flow channel, the sprayer is configured to spray a liquid upwardly from within the reservoir.
U.S. Pat. No. 6,827,036 describes aquaculture apparatus comprising an elongate tube of flexible translucent material, the tube extending longitudinally along a tube site and having a lower section defining a water course, and a cover extending externally over the tube and being air supported, said cover being at least partially spaced from the tube and providing an insulating space for insulating at least a substantial part of the tube.
U.S. Patent Application No. 20090130706 describes an enclosed photobioreactor configured to float on a body of water; the photobioreactor comprises: an elongated, longitudinally-oriented photobioreactor section constructed and arranged to contain a liquid medium comprising phototrophic organisms therein, the photobioreactor section comprises: a substantially flexible lower barrier comprising an upper surface in contact with and supporting the liquid medium; a cover constructed and arranged to cover the liquid medium within the photobioreactor section and further constructed and arranged to provide a gas headspace under the cover and above the liquid medium, the cover being at least partially transparent to light of a wavelength capable of driving photosynthesis; a first floatation element disposed on a first lateral side of the photobioreactor section; a second floatation element disposed on a second lateral side of the photobioreactor section; the first and second floatation elements being constructed and arranged to support the photobioreactor section for floatation on the body of water; and a plurality of tensioners constructed and arranged to apply tension to the lower barrier so as to maintain a substantial portion of the area of the lower barrier in a substantially horizontal configuration when the photobioreactor section is charged with the liquid medium, such that a continuous layer of the liquid medium has a substantially uniform depth which extends from approximately the first floatation element to approximately the second floatation element over at least a portion of the area of the lower barrier.
U.S. Patent Application No. 20100028976 describes a photobioreactor comprising: (a) a container adapted for holding fluid, comprising (i) opposing first and second sidewalls, wherein at least one of the first and second sidewalls is transparent; (ii) opposing first and second endwalls; (iii) a container bottom; and (iv) a container cover, wherein the first and second sidewalls comprise a plurality of separate sections, and wherein the separate sections are in fluid communication; (b) support struts for connecting the plurality of separate sections of the first and second sidewalls; (c) at least one inlet port in fluid communication with the container; (d) at least one outlet port in fluid communication with the container; (e) an aeration system in fluid communication with the container; and (f) a temperature control system connected to the container so as to control temperature of fluid within the container.
Reviews of technical problems connected with design of industrial photobioreactors are presented in the articles: James C. Ogbonna, Hideo Tanaka “Industrial-size photobioreactors” CHEMTECH 1997, 27(7), 43-49. and O. Pulz “PHOTOBIOREACTORS: PRODUCTION SYSTEM FOR PHOTOTROPHIC MICROORGANISMS” Springer-Verlag, 2001.
It should be noted that these US Patents and Patent Applications (including U.S. Pat. No. 5,981,271) do not solve construction problems of an elongated photobioreactor with length of some tens of meters to some hundreds of meters and with small inclination regarding the horizontal plane, wherein such photobioreactor is provided with effective means for enhancement of heat and mass transfer between the liquid and gaseous mediums in it.